I'm thinking of giving it Stockpile to boost both its defensive stats while giving it 45 Defense EVs and 213 HP EVs, while holding either Leftovers or Snorlium Z. (It's the exclusive gift Munchlax. I soft reset multiple times for its Nature.) Its last three moves I'm thinking would be Rest, Earthquake and Body Slam. Any suggestions and improvements to this idea would help a lot.
I'd reccomend Max HP and 4 on Sp.Def; seeing as you should be holding an eviolite until it evolves Stockpile and Slack off should be used over Rest, and after it evolves I'd reccomend switching Giga Impact for Return and having EQ as a last move; seeing as Gengar no longer has levitate in gen 7